Photonic Gel Films Hold Promise

By alternating layers of two different polymers - one rigid and glassy, the other soft and easily swollen with liquid or vapor - researchers funded by the National Science Foundation (NSF) report they've created photonic gel crystals that can be tuned to reflect light of many different colors across the visible and near-infrared spectrum.

The research results, reported in the Oct. 21 online issue of Nature Materials by Principal Investigator Edwin Thomas and his colleagues at the Massachusetts Institute of Technology's department of materials science and engineering, demonstrate the degree to which these photonic materials are tunable through changes in the soft layer's thickness and index of refraction. The responsiveness of the photonic crystals makes them likely candidates for active components of display, sensory or telecommunication devices.

"This is an ingenious and easy-to-implement method for making photonic materials whose optical properties can be readily tuned over a wide range [of the spectrum]," said Andrew Lovinger, director of the polymers program at NSF, which funded this research.

In one example, the researchers show very large, reversible optical changes by varying the salt content of a water solution in which these films are dipped. Multicolor patterns can be made by sequential coating of films, with the color of each region depending on the degree to which their molecules are chemically interconnected.

NSF funded the research in 2003 through a three-year grant aimed at creating new nanomaterials that are tunable through magnetic, chemical or other techniques. Following the discovery of intriguing new effects by Thomas and his colleagues involving the interaction of light and sound in these nanomaterials, his grant was extended for two additional years through a "special creativity award."

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2017, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards.